The invention relates to a method and a device for biologically treating a fluid which is sufficiently charged with organic materials, in particular waste waters, under anaerobic conditions and whilst generating biogas.
Waste water is the term used for water which has been changed after household, commercial and industrial use, in particular water which is contaminated and flows and passes into the drainage channels.
The biological treatment of highly charged liquids or the purification of waste water also represents a feature for removing organic contaminants from liquids, which contaminants are contained in the liquids in a dissolved, colloidal or finely dispersed form, by microbial activity, i.e. aerobic and/or anaerobic degradation forming gas whilst building up new cell substances and sorption of bacterial floc, biological lawns or sludge granulate.
Generally, waste water is biologically purified in waste treatment plants using the same or similar procedures which occur when the waste water biologically cleans itself in running waters, however, in a technically more intensive manner. The anaerobic process likewise occurs naturally, e.g. at the bottom of flat, still waters.
The term xe2x80x98anaerobic degradationxe2x80x99 is understood to mean the conversion of organic substances by means of micro-organisms whilst excluding oxygen. During the process of anaerobic degradation of organic substances biogas is produced, i.e. a gas mixture which consists approximately of 55 to 77% methane, approximately 24 to 44% carbon dioxide and traces of other ingredients.
Methods for biologically treating highly charged liquids under anaerobic conditions demand a relatively high specificity of the liquids. Such methods are suitable inter alia for highly charged liquids, in particular waste waters from the foodstuff industry, agriculture, mineral oil industry as well as from pulp making. In other words, they render it possible to treat many xe2x80x98concentratesxe2x80x99 but are generally incapable of providing a full purification or complete conversion.
A plant for the anaerobic treatment of waste water is known from the company Biothane Corporation (Company brochure, 7/92), which consists of a scaled, activated-sludge tank in which a group of separators are disposed in the upper region of the tank. In this plant, waste water is introduced via inlet orifices provided in the tank base into the activated-sludge tank and the treated waste water is discharged via a device provided in the upper region of the tank. This plant has inter alia the disadvantage that the reaction and secondary sedimentation regions are not spatially separate from each other and can therefore have a negative influence upon each other. For this reason the efficacy of the activated-sludge can also greatly reduce over a matter of time and problems can also occur when separating the sludge and the liquid.
Moreover, a plant for the anaerobic treatment of waste water is known from the company ADI Systems Inc. (company brochure, AS 043/11-94), which consists of a simple reaction tank which is upwardly sealed by means of a sheeting. This reaction tank is provided with a primary reaction region, the waste water being introduced from below into the sludge bed of the primary reaction region, a secondary reaction region and a secondary sedimentation region. Disposed between the primary and secondary reaction regions is a dipping wall which extends from the base of the reaction tank. The height of the dipping wall amounts to approximately ⅗ of the height of the reaction tank. Disposed between the secondary reaction region and the secondary sedimentation region are likewise dipping walls which extend downwards from the surface of the waste water. The height of these dipping walls amounts to approximately ⅓ of the height of the reaction tank. Moreover, the lower region of the secondary sedimentation region is provided with a discharge device for returning the sludge into the primary reaction region. One disadvantage of this plant resides in the fact that in particular the secondary reaction region is not sufficiently spatially separated from the secondary sedimentation region, which results in the efficacy of the sludge in the secondary reaction region considerably reducing over a matter of time. Also, the method performed in this plant does not take into consideration the different biological conditions in the two reaction regions. A further disadvantage of this method resides in the fact that the sludge in the second reaction region lies hardly used on the bottom.
The object of the invention was to provide a method and a device for biologically treating a fluid sufficiently charged with organic materials whilst producing biogas, the said method and device to guarantee an improved level of purification or degradation, an improved yield of methane gas, a considerably more favourable investment and a more reliable operation.
The advantages of the invention reside in the fact that owing to its compact structure with an integrated gas reservoir the device in accordance with the invention provides a considerable saving as far as space and costs are concerned (inter alia owing to savings made in insulating material) and furthermore is earthquake safe and is independent regarding settling.
According to the present invention the term xe2x80x98fluids sufficiently charged with organic materialsxe2x80x99 is understood to mean blood, liquid manure and preferably waste waters, which comprise, for example, the following parameters:  greater than ca. 2000 mg BSB5/l (in cooler climates) and  greater than ca. 500 mg BSB5/l (in warmer climates).